Electronic control of an automotive internal combustion engine frequently requires measurement or calculation of the air flow to the engine. For many engines, such air flow is determined by a rotatable valve disposed in the engine air induction passage. In some applications the valve is a throttle valve which is positioned by an operator to determine or control air flow to the engine. In other applications the valve is an air valve the position of which is regulated to determine or measure air flow to the engine. With either type of valve, air flow to the engine varies as a function of the air flow area around the valve and the pressure difference across the valve.
Because the air flow area around such a valve is geometrically related to the position of the valve, valve position is often sensed as a basis for measuring or calculating air flow to the engine. In a conventional induction air flow valve assembly, however, the change in the air flow area around the valve for a selected rotation of the valve is much greater when the valve is near its minimum air flow position than when the valve is near its maximum air flow position, and calibration of the valve position sensor is thereby complicated. Structures which would offer a relatively low normalized change in the air flow area around the valve have required manufacturing techniques which, at least in some cases, have not been compatible with the flat butterfly valve conventionally used to determine air flow to internal combustion engines.